GL_SGIX_shadow http://oss.sgi.com/projects/ogl-sample/registry/SGIX/shadow.txt GL_SGIX_shadow GL_TEXTURE_COMPARE_SGIX 0x819A GL_TEXTURE_COMPARE_OPERATOR_SGIX 0x819B GL_TEXTURE_LEQUAL_R_SGIX 0x819C GL_TEXTURE_GEQUAL_R_SGIX 0x819D